There is very little difference. This is exactly the kind of question that makes a NATIVE speaker goes to a dictionary! My favorite is ahdictionary.com . The people who write dictionaries are very clear and thoughtful about writing definitions. But I will try to answer off the top of my head. These are just rough answers. "Normal" has the idea of "the way things are supposed to be." There's a value judgement. "Normally, we cover our mouths when we cough." Whether or not people do it, it's the right thing to do. "Regular" suggests a default, what you get if you don't ask for something different. "Get some bread." "Anything special?" "No, just regular bread, any brand." I think "ordinary" is a close synonym. "General" is the opposite of "special." "Common" in ordinary speech suggests frequent, or present in a high percentage. "Nowadays it is common for people to have cell phones." Most people have them.